The present invention relates, in general, to a pipe bend for a pipeline for transport of abrasive materials.
Pipelines, comprised of individual pipe members, such as pipe bends and/or straight pipes, for transport of abrasive materials, such as, e.g. sand or concrete, have to meet high demands. On the one hand, the pipe members and in particular the pipe bends of different curvature, which are incorporated in the pipeline, should have inner surfaces that are highly wear-resistant. On the other hand, the pipe members should be of a material sufficient to withstand impacts and shocks, without crack formations. In other words, the pipe members should have a hard inside surface and a soft outside surface.
In order to reconcile these contradicting requirements, pipe members for pipelines have been configured of two layers. The inner layers are hardened at least over a major part of their radial thickness, while the outer layers are made of weldable steel. In this way, the outer layers could also be connected at their ends with coupling collars for respective attachment of two pipe members. These coupling collars are designed with their end faces at a right angle to the longitudinal axes so that, after removal of a, normally split, coupling clamp, a worn-out pipe member can be withdrawn in radial direction from the pipeline and replaced by a new pipe member, without requiring the pipeline to be pulled apart in axial direction.
So long as straight pipe members are involved, this proposal has proven to be useful. However, when pipe bends are involved, this configuration suffers shortcomings as pipe bends are exposed to much higher wear, when the transported material changes the flow direction.
Conventionally, the terminal coupling collars are each comprised of an outer ring, which is formed with an outer circumferential anchoring groove, and an inner ring, which is surrounded by the inner ring and made of more wear-resistant material than the outer ring. The inner ring is secured against axial displacement solely in the direction toward the end faces of the pipe bends. In view of unavoidable manufacturing tolerances, the internal components of the pipe bends, i.e. inner rings and inner layers, are installed at relative clearance, so that the pressure of the transported material causes a shift of the trailing inner rings, together with the inner layers, in the direction towards the leading inner rings, as viewed in material flow direction. Therefore, the gap already provided between the trailing inner rings and inner layers as a result of manufacturing tolerances, widens further between two successive pipe bends. This significantly adversely affects the service life of the pipe bends with the internal components shifted in flow direction.
In addition, in situations when a worn-out seal between two pipe bends must be replaced, and the installer has to replace the trailing pipe bend, as viewed in material flow direction, the gap between adjacent pipe bends is further widened, when the installer mounts the pipe bend in inverse disposition, because the internal components that have shifted in flow direction are cemented tight in their shifted position by the materials. As a consequence, wear is even greater in the transition area from one pipe bend to the neighboring pipe bend.
It would therefore be desirable and advantageous to provide an improved pipe bend which obviates prior art shortcomings and which exhibits high wear resistance and yet is easy to replace and easy to fabricate.
According to one aspect of the present invention, a pipe bend for a pipeline for conveying abrasive materials, such as sand or concrete, includes a pair of coupling collars including an outer ring, which has an outer circumferential anchoring groove, and an inner ring mounted in the outer ring and secured therein against displacement in axial direction, wherein the inner ring is made of a material which is more wear-resistant than a material of the outer ring; an arcuate outer pipe portion extending between the coupling collars and having opposite ends welded to the outer ring of the coupling collars, wherein the outer pipe portion has an inner diameter which is greater than an inner diameter of the outer rings of the coupling collars; and an arcuate inner pipe portion extending at a radial distance to the outer pipe portion between the inner rings of the coupling collars and made of a material which is more wear-resistant than a material of the outer pipe portion, wherein the inner pipe portion has opposite ends of an inner cross section which is in coaxial alignment to an inner cross section of the inner rings, for radial support upon the outer pipe portion.
Although being disposed at comparably great distances to the outer pipe portion in radial direction and to the inner rings of the coupling collars in axial direction, the inner pipe portion can still be reliably integrated in the outer pipe portion, despite imprecisions during fabrication, in such a manner that the terminal inner cross sections of the inner pipe portion are disposed in accurate coaxial alignment with respect to the inner rings of the coupling collars. Radial offsets or stepped shoulders between the inner pipe portion and the inner rings, which would be exposed to increased wear and thus would shorten the service life of the pipe bend can be avoided.
Exact alignment of the terminal inner cross sections of the inner pipe portion with the inner cross sections of the inner rings can be realized by inserting centering pins into the coupling collars from the end faces of the pipe bend, and subsequently radially supporting the inner pipe portion against the outer pipe portion. After removing the centering pins, the inner pipe portion is accurately aligned with the inner rings of the coupling collars. In this way, the pipe bend is not heavier than conventional pipe bends but has a much longer service life.
In view of the fact that the inner rings are secured in position in the outer rings of the coupling collars and the inner pipe portion is secured in position in the outer pipe portion, the internal components of a pipe bend according to the present invention can no longer shift as a consequence of exerted pressure by the conveyed material. A pipe bend according to the present invention has not only a higher wear resistance at the ends of the pipe bend, but it is also immaterial whether the pipe bend is installed in 180xc2x0 rotated disposition after replacement or a change of seals, so that greater gap formation and accompanying increased wear are no longer an issue.
The axial securement of the inner rings in the outer rings of the coupling collars may be realized by mounting the inner ring of each coupling collar to the outer ring between an inwardly directed shoulder at one end of the outer ring and a radially inwards directed constraint at the other end of the outer ring. As the outer ring is welded to the outer pipe portion, the shoulder can be made through a turning process. The respective inner ring is then inserted in the outer ring until abutting the shoulder. The constraint at the other end face may be a radially inwardly directed flange, which extends about the entire circumference, or tabs arranged at predetermined areas and projecting radially inwards, for precisely clamping the inner ring in axial direction.
According to another feature of the present invention, spacers may be provided for securing the inner pipe portion in radial relationship to the outer pipe portion. The spacers may be pins of steel and maintain a required distance of the inner pipe portion from the outer ring in a simple and reliable manner, despite imprecisions during the manufacturing process. The spacers are suitably driven in boreholes of the outer pipe portion so as to be fixed in place and thereby secure a position of the inner pipe portion relative to the outer pipe portion, with the spacers merely abutting the outer surface of the inner pipe portion. Optionally, the spacers may additionally be fixed to the outer pipe portion by a welding process.
According to a variation of the present invention, the inner pipe portion may be secured in radial relationship to the outer pipe portion through spot introduction of a fast curing pasty mass into an annular space between the outer and inner pipe portions via boreholes formed in the outer pipe portion at predetermined locations. In this way, the inner pipe portion is radially secured in place with respect to the outer pipe portion, whereby the annular space between the inner and outer pipe portions is effective, despite imprecisions during the manufacturing process. Examples for the pasty mass include multi-component concrete based on plastic. The mass thus fills the annular space between the inner and outer pipe portions in the area of the boreholes and forms a supporting bridge between the inner and outer pipe portions.
Although it is normally sufficient to fix the inner pipe portion relative to the outer pipe portion in radial direction at predetermined points, it is of course conceivable to inject enough pasty mass via the boreholes to fill, or at least to partially fill, the entire space between the inner and outer pipe portions. Suitably, the boreholes for introduction of pasty mass may be plugged by inserts, made, for example, of steel, which may be secured in the boreholes through a press fit. The length of the inserts may correspond to the wall thickness of the outer pipe portion. Of course, the inserts may be secured in place in the boreholes of the outer pipe portion by other means, e.g. through a welding process.
According to another feature of the present invention, the spacers or the boreholes for introduction of pasty mass are arranged in two axially spaced-apart cross sectional planes at 120xc2x0 offset relationship in each of the cross sectional planes, thereby realizing a proper positioning of the inner pipe portion with respect to the outer pipe portion. Of course, persons skilled in the art will understand that the spacers or the boreholes may also be arranged in more than two cross sectional planes at circumferential offset relationship which may also be smaller or greater than 120xc2x0.
According to another feature of the present invention, the outer ring of each of the coupling collars and the outer pipe portion are made of weldable steel, and the inner ring of each of the coupling collars and the outer pipe portion are made of curable plastics. Examples of cast steel include a chromium carbide based casting material. As cracks caused by stress cannot be avoided, when chromium carbide based casting material is involved, so that inner rings made of such material are very susceptible to fracture, the precise axial securement of the inner rings between the shoulders and the flanges still ensures a full operativeness of the inner rings, even when made of chromium carbide based casting material.
The gap formed between the inner pipe portion, inner rings and outer pipe portion are normally filled quickly during operation by the material being conveyed, so that, in effect, a padding is formed to additionally support the more wear-resistant inner pipe portion with respect to the softer material of the outer pipe portion.
According to another feature of the present invention, the annular space between the outer and inner pipe portions may also be filled with curable plastics. In this way, the inner pipe portion is properly supported already during fabrication of the pipe bend and during transport. In addition, possible material deposits in the annular space are prevented which may cause a deformation of the outer pipe portion, in particular when weight consideration dictate an outer pipe portion of comparably thin wall thickness. Plastic material may be injected in the annular space between the inner and the outer pipe portions via at least one opening which can be subsequently sealed again, for example, through welding, press-fitted pin or welded pin.